A powder molding machine, as shown in FIG. 5, forcibly presses molding powder filled into a molding space (cavity) 3 of a die 2 by a punch (only a lower punch 14 is shown in FIG. 5), thus producing molded products. A feed shoe 1 is used for filling the molding powder into the aforesaid molding space 3.
The die 2 is usually mounted on a plate 27 having a flat surface so that the top surface of the die becomes flush with that of the plate. The feed shoe 1 is linearly reciprocated in the front and rear direction while sliding on the aforesaid plate 27. As seen from the cross-sectional view shown in FIG. 5, the feed shoe 1, having a shape just like that of an upside-down bowl, stores molding powder in its interior, and drops the molding powder stored in the interior into the molding space 3 of the die 2 as the feed shoe advances. The molding powder is always supplied from a hopper (not shown) located above the feed shoe 1 through a flexible hose 36.
After the feed shoe 1 is advanced to supply the molding powder S into the molding space 3 of the die, and is then retreated from the molding space 3, the surface of molding powders filled in the molding space 3 of the die becomes undulate. This is because portions having high density and low density appear almost like waves in the filled powder S. This is caused by the following reason: when the feed shoe 1 is retreated, a plurality of swirls, which rotate in a specific direction such as the moving direction of the feed shoe 1, are made in the powder filled in the interior of the feed shoe 1, as shown in FIG. 5, and these swirls disturb the uniformity of density of the molding powder filled in the molding hollow space 3 of the die 2. In particular, in the case where the depth of molding space 3 is shallow, the powder uniformly filled is easy to be disturbed when the feed shoe is retreated. For this reason, the density of the front-side portion of the powder S filled in the molding space 3 becomes low; on the other hand, the density of the rear-side portion of the powder S becomes high.
As described above, if the powder filled in a state in which the density is not uniform is pressed by means of a punch, the density of molded products thus obtained has a non-uniform density, and its strength lowers.